The present invention relates to a valve, a pressure control valve in particular, with a valve housing having pump, appliance and tank connections. A valve piston can be driven by a magnetic inductor for guided movement within the valve housing.
Conventional proportional pressure control valves are used, among other things, as control valves for oil-hydraulic systems to deliver a more or less constant output pressure with variable input pressure. The output pressure to be controlled is assigned by the current signal delivered by suitable triggering electronics and acting on an actuating magnet. The actuating magnet may be designed as a pressure sealed oil bath magnet with a long service life.
Proportional pressure control valves serving this purpose may be directly controlled piston valves of a three-way design, that is, with pressure protection on the output side. They are employed, among other things, in oil-hydraulic systems to control couplings, in shift transmissions for exerting a specific pressure buildup and pressure reduction effect, for remote pressure adjustment, for control of pressure variation over time and for pilot control of hydraulic valves and logic elements.
Conventional proportional pressure control valves employed for these purposes are characterized by poor stability, especially in the case of low-viscosity fluid media. They begin to vibrate, something especially harmful if the conventional valves are to perform special functions, for example, in motor vehicle power steering systems, areas relating to safety engineering, or the like. Generally, susceptibility to disturbances has been found to occur in the natural frequency range of the valve. The instabilities arising may result in functional failure of a valve and the relevant parts of its system.
Objects of the present invention are to provide improved valves with more stable behavior, in particular with respect to steady-state vibrations, so that the valve is also well suited for special appliances.
The valve according to the present invention is provided with a hydraulic damping device having a damping chamber connected by a throttle to the connection of the appliance to convey fluid. Optionally, the pump connection or tank connection communicates with the appliance connection. In the event of displacement of the valve piston toward the choke as a result of the magnetic force of a switching magnet, the fluid stored in the damping chamber is displaced toward the appliance connection by the throttle. The displacement volume flow generates local pressure buildup by the throttle. A force directed against the deflecting force of the valve piston onto the effective pressure surface adjoining the flow restriction point may be determined. Thus, a damping effect may be exerted on the entire valve piston. As the valve piston travels back in the opposite direction, this volume of fluid must flow back away from the appliance connection into the damping space, now increasing, again by of the throttle as defined. This flow also results in damping of the vibrations which occur.
In a preferred embodiment of the valve of the present invention, the throttle is in the form of a ring disk which impedes the flow of fluid between damping space and appliance connection by a flow restriction point. In one embodiment of the valve of the present invention, the flow restriction point may be in the form of a through opening inside the ring disk. Preferably, however, in an alternative embodiment, the flow restriction point is at least in part in the form of an annular passage formed between the ring disk and parts of the valve housing surrounding the ring disk. The latter solution improves damping results and can be applied cost effectively during manufacture.
In addition, the annular passage can discharge into a connecting duct of the ring disk communicating with to the damping space to conduct fluid. The ring disk can be flange-connected to the valve housing at various points, the annular passage being interrupted at the connection points, just as it is by frontal mounting of the annular passage in the interior of the valve housing. A simple yet functionally reliable connection of the throttle to the remaining portion of the valve housing is obtained in this manner.
In another especially preferred embodiment of the present invention, the connecting line extends at least in part parallel to the direction of advance of the valve piston inside the valve housing. This piston optionally makes connection with the tank or with the pump connection. As a result of the connecting line, the functional component proper of the valve is separated from the damping component, and, as a result, the functional reliability of the valve design is increased.
Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.